Osmotic adaptation is a fundamental problem in cell biology. Recent work in our own and other laboratories has provided strong evidence for the important role of membrane-derived oligosaccharides (MDO) of E. coli in osmotic adaptation and cell signalling, and for the functions of the closely similar periplasmic cyclic glucans of the Rhizobiaceae. This application is focussed on the MDO of E. coli with the following specific goals. I. THE BIOSYNTHESIS OF MDO A. The Function of ACP B. The Function of Polyprenol Derivatives C. Search for Protein-bound Intermediates II. GENETIC REGULATION OF MDO BIOSYNTHESIS A. Enzyme Activities and mdo Phenotypes B. Search for in vitro Complementation C. Mapping of mdo Mutations III. MECHANISM OF OSMOTIC REGULATION OF MOD SYNTHESIS A. Time Course of Osmotic Adaptation B. Osmotic Regulation of Enzyme Levels C. Feedback Inhibition of MDO Synthesis